1. Field of the Invention
The present invention relates to a piston type compressor. More particularly, the present invention relates to a piston type compressor in which the quality of the seal at the end face of a cylinder block has been improved. The piston type compressor of the present invention can be preferably used for an air conditioner in a vehicle.
2. Description of the Related Art
A conventional piston type compressor used for an air conditioner in a vehicle (referred to simply as a xe2x80x9ccompressorxe2x80x9d hereinafter) comprises a cylinder block in which a cylinder bore is formed internally, a front housing that supports a drive shaft while allowing a rotational motion and is coupled to a front of the cylinder block at a front coupling surface, which is formed by a rear end face of the front housing and a front end face of the cylinder block and has an outer periphery, and a rear housing that forms a suction chamber and a discharge chamber internally and is coupled to the rear of the cylinder block at a rear coupling surface, which is formed by a front end face of the rear housing and a rear end face of the cylinder block and has an outer periphery.
In a compressor of this type, by means of a reciprocating motion of pistons in cylinder bores, refrigerant at low pressure, which has been fed back to the suction chamber from an external refrigerating circuit, is sucked into the cylinder bores and compressed and then discharged into the discharge chamber as high pressure refrigerant.
Such a compressor, however, has a problem that its performance is degraded due to the loss of the refrigerant gas to be compressed, if the high pressure refrigerant gas leaks out of the compressor through the cylinder block end face when the refrigerant gas at low pressure is compressed in the cylinder bore, or when the compressed high pressure refrigerant gas is discharged from the cylinder bore to the discharge chamber.
The above-mentioned problem becomes more conspicuous particularly in an air conditioner in which the pressure of the high-pressure side (discharge pressure of the compressor) of a closed circuit, a constituent part of the air conditioner, reaches a supercritical pressure of the refrigerant. (Such an air conditioner will be referred to as an xe2x80x9cair conditioner with a supercritical cyclexe2x80x9d hereinafter).
In a compressor of an air conditioner with a supercritical cycle, refrigerant gas is compressed beyond its critical pressure For example, when carbon dioxide that has a critical pressure of about 7.35 MPa is used as refrigerant, it will be compressed to a pressure of about 10 MPa. On the other hand, in an air conditioner that uses refrigerant of chlorofluorocarbon type, in which both the discharge pressure and the suction pressure are below the critical pressure of the refrigerant during operation (such an air conditioner will be referred to as an xe2x80x9cair conditioner with subcritical cyclexe2x80x9d hereinafter), the discharge pressure of the compressor is about 1 to 3 MPa, and it can be concluded that the discharge pressure of a compressor in an air conditioner with a supercritical cycle is by far higher than that in an air conditioner with subcritical cycle. In a compressor of an air conditioner with supercritical cycle, therefore, the high pressure refrigerant may leak easily through the end face of the cylinder block because of the high pressure.
Particularly when carbon dioxide is adopted as refrigerant, it is difficult to achieve a sufficient sealing performance because of the high permeability of the carbon dioxide through rubber, even though O-rings are used at the end face of the cylinder block for sealing.
With these above-mentioned problems being taken into account, the present invention has been developed. The technical purpose of the present invention is to prevent the degradation of the performance of a compressor due to the leakage of refrigerant gas by preventing the high pressure refrigerant from leaking out of the compressor through the end face of the cylinder block.
The piston type compressor in the first aspect of the present invention comprises a cylinder block which has cylinder bores formed therein, a rear end face and a front end face, a front housing that has a rear end face, supports a drive shaft while allowing a rotational motion and is coupled to a front of the cylinder block at a front coupling surface, which is formed by the rear end face of the front housing and the front end face of the cylinder block and has an outer periphery, and a rear housing that has a front end face and forms at least a discharge chamber internally and is coupled to a rear of the cylinder block at a rear coupling surface, which is formed by the front end face of the rear housing and the rear end face of the cylinder block and has an outer periphery, wherein: refrigerant is compressed and the high pressure refrigerant is discharged to the discharge chamber by the reciprocating motion of pistons in the cylinder bores by driving the drive shaft; and at least one of the front housing and the rear housing includes a cylindrical wall that is placed radially outside and encloses the front coupling surface and the rear coupling surface.
In this compressor, the front coupling surface, which is formed by the front end face of the cylinder block and the rear end face of the front housing, and the rear coupling surface, which is formed by the rear end face of the cylinder block and the front end face of the rear housing are enclosed by the cylindrical wall placed radially outside of them, and the inside of the compressor is isolated from the outside air. Therefore the sealing ability at the front coupling surface and the rear coupling surface has been improved. The seal can prevent the high pressure refrigerant in the cylinder bore and the discharge chamber from leaking through the front coupling surface and the rear coupling surface, when the high pressure refrigerant compressed in the cylinder bore is discharged to the discharge chamber according to the reciprocating motion of the pistons in the cylinder bores by driving the drive shaft. As explained above, the degradation of the performance of the compressor due to the leakage of the high pressure refrigerant through the front coupling surface and the rear coupling surface, that is, out of the compressor through the end face of the cylinder block, can be avoided.
Furthermore, since the above-mentioned cylindrical wall is attached at least to one of the front housing and the rear housing, it is not necessary to provide a part such as a cylindrical wall, separately, to enclose the front coupling surface and the rear coupling surface, leading to an advantage in cost and in simplicity of structure.
Still furthermore, even if such parts as O-rings are removed, which serve to seal the front coupling surface and the rear coupling surface, the high pressure refrigerant can be prevented from leaking out of the compressor, and the cost can also be reduced and the structure can be simplified due to a reduction in the number of parts.
The piston type compressor in the second embodiment of the present invention comprises a cylinder block which has a cylinder bore formed therein, a rear end face and a front end face, a front housing that has a rear end face, supports a drive shaft, while allowing a rotational motion, and is coupled to a front of the cylinder block at a front coupling surface, which is formed by the rear end face of the front housing and the front end face of the cylinder block and has an outer periphery, a rear housing that has a front end face forms at least a discharge chamber internally and is coupled to a rear of the cylinder block at a rear coupling surface, which is formed by the front end face of the rear housing and the rear end face of the cylinder block and has an outer periphery, and a motor housing placed in front of the front housing and equipped internally with a motor mechanism that drives the drive shaft, wherein: refrigerant is compressed and the high pressure refrigerant is discharged to the discharge chamber by the reciprocating motion of pistons in the cylinder bores by driving the drive shaft; the motor housing includes a cylindrical wall that is placed radially outside and encloses the front coupling surface and the rear coupling surface; and a cover member, which is placed behind a rear of the rear housing, and the front end face of which comes into contact with the rear end face of the rear housing, is coupled to a rear end of the cylindrical wall.
In this compressor, the front coupling surface and the rear coupling surface are enclosed by the cylindrical wall of the motor housing, and the inside of the compressor is isolated from the outside air, thus the sealing ability at the front coupling surface and the rear coupling surface is improved. At the same time, a hermetic space is formed internally by coupling the cylindrical wall of the motor housing to the cover member. Therefore the seal can prevent the high pressure refrigerant in the cylinder bores and the discharge chamber from leaking through the front coupling surface and the rear coupling surface, when the high pressure refrigerant compressed in the cylinder bores is discharged to the discharge chamber by the reciprocating motion of the pistons in the cylinder bores by driving the drive shaft by the motor mechanism. Moreover, even if the high pressure refrigerant leaks through the front coupling surface and the rear coupling surface, the leaked high pressure refrigerant remains in the hermetic space formed by coupling the cylindrical wall to the cover member and does not leak out of the compressor. As explained above, the degradation of the performance of the compressor due to the leakage of the high pressure refrigerant out of the compressor through the front coupling surface and the rear coupling surface can be avoided.
Furthermore, since the above-mentioned cylindrical wall is attached to the motor housing, it is not necessary to provide a part such as a cylindrical wall separately to enclose the front coupling surface and the rear coupling surface, leading to advantages in cost and in simplicity of structure.
Still furthermore, since the hermetic space is formed internally by coupling the cylindrical wall of the motor housing to the cover member, the reliability of the seal in the compressor can be improved by improving the reliability of the seal between the coupling surfaces of the cylindrical wall and the cover member.
Moreover, even if such parts as O-rings, which serve to seal the front coupling surface and the rear coupling surface, are removed, the high pressure refrigerant can be prevented from leaking out of the compressor, and the cost can be reduced and the structure can be simplified due to the reduction in the number of the parts.
Moreover, since the front end face of the cover member comes into contact with the rear end face of the rear housing, the cover member can securely prevent the rear housing, which receives the high pressure in the discharge chamber, from detaching from the cylinder block. Therefore, a higher quality seal at the rear coupling surface can be maintained by maintaining a higher tightness, compared with the case when the front end face of the cover member does not come into contact with the rear end face of the rear housing.
The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below, together with the accompanying drawings.